Comments on: Dirty DWI Secrets

By: Windypundit

Windypundit — Thu, 26 Jun 2008 23:01:08 +0000

No, I couldn't find that data, but in a more recent post I linked to an NHTSA summary report and a study from that report that attempts to estimate relative risk as a function of BAC, which I think is what we really want to know. I'm not sure I really understood it, though. Check it out.

By: Gritsforbreakfast

Gritsforbreakfast — Thu, 26 Jun 2008 18:26:49 +0000

I didn’t mean to be critical, btw, just was suggesting ways to follow up to complete the analysis. I think where you’ve gotten with it so far is valid and useful.

Windy, any footnote giving average miles per trip in the data you got that stuff from? If so, you might be able to get to an apples to apples estimate through the back door.

Once you get that figure, simple subtraction will get you to the ADDED risk of accidents from DWI.

By: Mark Bennett

Mark Bennett — Thu, 26 Jun 2008 16:54:25 +0000

Excellent points. I don’t think Windy assumed that all alcohol-related accidents were caused by alcohol; I think he took NHTSA’s number for accidents with an intoxicated driver (which is half the alcohol-related number) instead, noting that this was probably high.

When you pay $43.85 to take a cab home and then back to your car the next day, you’re still risking causing (indirectly) someone else’s death or injury (are cabbies less safe or safer than sober non-cabbies?). You’re paying to eliminate only the risk of a DWI arrest.

If we could somehow figure how much more likely an intoxicated person is than a sober one to injure or kill someone per mile driven, and the cost of doing so, we might rationally call a stretch limo instead of a cab.

I can believe that a sober teenager might be a greater danger to himself and others than an intoxicated adult.

By: Windypundit

Windypundit — Thu, 26 Jun 2008 16:36:20 +0000

Good points, Grits, especially about using miles travelled. I’m just too lazy to try to track that down. I imagine it must be hard to get accurate self-reported survey results for miles driven drunk.

I know I should have been more careful to look at excess deaths, but I wanted to err in favor of greater danger to avoid being accused of twisting the stats in my favor.

By: Gritsforbreakfast

Gritsforbreakfast — Thu, 26 Jun 2008 14:53:06 +0000

Interesting data. But you’d need a baseline number for non-alcohol related injury accidents to compare it to. Most accidents happen involving no alcohol at all, so the assumption that all alcohol-involved incidents were caused by alcohol likely overstates the risk.

According to the NHTSA report you linked to, there were around 38,000 accident fatalities in 2004. If 8K were DWI-related, that means around 30K were not. Even citing the higher number used by MADD, the report said “The percent of alcohol-related fatalities has declined from 60 percent in 1982 to 39 percent in 2004″

NHTSA uses miles traveled as their denominator for calculating frequency instead of the number of self-reported trips used by Windy, so I couldn’t find apples to apples numbers to compare offhand. But whatever the per-trip injury-crash rate for non-alcohol related accidents is should be subtracted from the DWI rate you calculated to identify how much EXTRA risk using alcohol imposes.

Judging by other data in the NHTSA report, another good question is whether sober teenage boys pose a greater risk than an adult drunk! The stats on age and gender breakdowns of accidents make one (momentarily) sympathetic with insurance actuaries!

Good post and series!

By: Windypundit

Windypundit — Thu, 26 Jun 2008 14:49:24 +0000

Great post, especially about accident rates.

(And I plugged your math into my spreadsheet, and it’s fine.)